Theresa May has insisted a Labour election victory "could happen" as she warned Conservative supporters in Wales against complacency.
The prime minister said every vote in the election will count as she battled for votes in Labour's traditional heartland.
"Remember the opinion polls were wrong in the 2015 general election, they were wrong in the referendum last year," Mrs May said.
"Jeremy Corbyn himself has said he was a 200-1 outsider for the Labour leadership in 2015 and look where that one went. So we must not be complacent and I'm not complacent."
Mrs May said the General Election was "the most important election this country has faced in my lifetime" as she addressed supporters in the marginal seat of Bridgend.
Madeleine Moon MP's seat is the Conservatives' top target in Wales as she defends a 1,927 majority that is Labour's second smallest in the country.
Mrs May accused nationalists of "propping up" Labour in Wales in a deal that shows how "collaboration" between smaller parties could put Mr Corbyn into power.
"A vote for any other party would be a vote for a weak and failing Jeremy Corbyn propped up by a coalition of chaos which would risk our national future," she said.
The PM left the door open to tax breaks for workers that would be viewed as a direct pitch to sway Labour voters in areas like Wales.
Amid reports the party is considering the tax "sweetener" for working people, she said: "There's a choice between a Conservative Party which always has been, is and will always be a party that believes in lower taxes."
She added: "The choice is between that and a Labour Party whose natural instinct is always to put up taxes."
Mrs May's pitch for votes came as Welsh First Minister Carwyn Jones warned Labour had a mountain to climb.
The Welsh Labour leader urged Jeremy Corbyn to produce a manifesto with the "widest possible appeal", saying the party must show it has a "programme for government" and is not simply a "protest group".